An electron microscope is a type of microscope that uses electrons to illuminate a specimen and create an enlarged image. A microscope ( Greek: ( micron) = small + ( skopein) = to look or see is an instrument for viewing objects that are The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J Electron microscopes have much greater resolving power than light microscopes and can obtain much higher magnifications. Angular resolution describes the resolving power of any image forming device such as an optical or Radio telescope, a Microscope, a Camera The optical microscope, often referred to as the "light microscope" is a type of Microscope which uses Visible light and a system of lenses to Magnification is the process of enlarging something only in appearance not in physical size Some electron microscopes can magnify specimens up to 2 million times, while the best light microscopes are limited to magnifications of 2000 times. Both electron and light microscopes have resolution limitations, imposed by their wavelength. The greater resolution and magnification of the electron microscope is due to the wavelength of an electron, its de Broglie wavelength, being much smaller than that of a light photon, electromagnetic radiation. The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J In Physics, the de Broglie hypothesis (pronounced /brœj/ as French breuil close to "broy" is the statement that all Matter (any object has a Wave Light, or visible light, is Electromagnetic radiation of a Wavelength that is visible to the Human eye (about 400–700 Electromagnetic radiation takes the form of self-propagating Waves in a Vacuum or in Matter.

The electron microscope uses electrostatic and electromagnetic lenses in forming the image by controlling the electron beam to focus it at a specific plane relative to the specimen in a manner similar to how a light microscope uses glass lenses to focus light on or through a specimen to form an image. An electrostatic lens is a device that assists in the transport of Electrons emitted from a sample to an Electron analyzer, analogous to the way an optical lens Electromagnetism is the Physics of the Electromagnetic field: a field which exerts a Force on particles that possess the property of

History

An image of an ant from a scanning electron microscope

The first electron microscope prototype was built in 1931 by the German engineers Ernst Ruska and Max Knoll. Ants are social Insects of the family Formicidae and along with the related families of Wasps and Bees belong to the order Year 1931 ( MCMXXXI) was a Common year starting on Thursday (link will display full 1931 calendar of the Gregorian calendar. Ernst August Friedrich Ruska ( December 25, 1906 &ndash May 27, 1988) was a German physicist. Max Knoll ( 17 July 1897 &ndash 6 November 1969) was a German Electrical engineer. ^[1] It was based on the ideas and discoveries of French physicist Louis de Broglie. Louis-Victor-Pierre-Raymond 7th duc de Broglie, FRS (də bʁœj ( August 15 1892 &ndash March 19 1987) was a French Although it was primitiveand not fit for practical use, the instrument was still capable of magnifying objects by four hundred times.

Reinhold Rudenberg, the research director of Siemens, had patented the electron microscope in 1931, although Siemens was doing no research on electron microscopes at that time. Reinhold Rudenberg ( February 4, 1883 – December 25, 1961) was a German-American Electrical engineer and Inventor, credited In 1937 Siemens began funding Ruska and Bodo von Borries to develop an electron microscope. Siemens also employed Ruska's brother Helmut to work on applications, particularly with biological specimens. Helmut Ruska ( June 7, 1908 - August 30 1973) was a German physician and Biologist from Heidelberg. ^[2][3]

In the same decade of 1930s Manfred von Ardenne pioneered the scanning electron microscope and his universal electron microscope. Manfred von Ardenne ( January 20, 1907 in Hamburg - May 26, 1997 in Dresden) was a German research and applied The scanning electron microscope ( SEM) is a type of Electron microscope that images the sample surface by scanning it with a high-energy beam of Electrons ^[4]

Siemens produced the first commercial TEM in 1939, but the first practical electron microscope had been built at the University of Toronto in 1938, by Eli Franklin Burton and students Cecil Hall, James Hillier, and Albert Prebus. This article is about the University of Toronto's St George Campus Year 1938 ( MCMXXXVIII) was a Common year starting on Saturday (link will display the full calendar of the Gregorian calendar. Eli Franklin Burton, FRSC ( February 14, 1879 &ndash July 6, 1948) was a Canadian physicist. Not to be confused with the British actor James Hillier (actor. ^[5]

Although modern electron microscopes can magnify objects up to two million times, they are still based upon Ruska's prototype. A prototype is an original type form or instance of something serving as a typical example basis or standard for other things of the same category The electron microscope is an integral part of many laboratories. Researchers use it to examine biological materials (such as microorganisms and cells), a variety of large molecules, medical biopsy samples, metals and crystalline structures, and the characteristics of various surfaces. A microorganism (also spelled micro organism or micro-organism and also called a microbe) is an Organism that is Microscopic (usually The cell is the structural and functional unit of all known living Organisms It is the smallest unit of an organism that is classified as living and is often called In Chemistry, a molecule is defined as a sufficiently stable electrically neutral group of at least two Atoms in a definite arrangement held together by A biopsy (in Greek: βίος life and όψη look/appearance is a Medical test involving the removal of cells or tissues The M acro E xpansion T emplate A ttribute L anguage complements TAL, providing macros which allow the reuse of code across In Materials science, a crystal is a Solid in which the constituent Atoms Molecules or Ions are packed in a regularly ordered repeating The electron microscope is also used extensively for inspection, quality assurance and failure analysis applications in industry, including, in particular, semiconductor device fabrication. Semiconductor device fabrication is the process used to create chips the Integrated circuits that are present in everyday Electrical and electronic

Electron microscope manufacturers

Major manufacturers include:

• Aspex Corporation
• Delong Group
• FEI Company – USA (merged with Philips Electron Optics)
• FOCUS GmbH – Germany
• Hitachi – Japan
• Nion Company - USA
• JEOL Ltd. – Japan (Japan Electro Optics Laboratory)
• TESCAN – EU
• Carl Zeiss NTS GmbH - Germany

Types

Transmission Electron Microscope (TEM)

Main article: Transmission electron microscopy

The original form of electron microscopy, Transmission electron microscopy (TEM) involves a high voltage electron beam emitted by a cathode, usually a tungsten filament and focused by electrostatic and electromagnetic lenses. Aspex Corporation, originally founded in 1992, is a supplier of Electron microscopy tools to researchers developers and manufacturers working on Process FEI Company ( founded in 1971 is a supplier of Electron microscopy tools to researchers developers and manufacturers working on the nanoscale. Koninklijke Philips Electronics NV ( Royal Philips Electronics Inc. () is a Multinational corporation specializing in high-technology and services headquartered in Marunouchi Itchome Chiyoda, Tokyo, Japan. is a notable manufacturer of Electron microscopes and other scientific instruments Electrical tension (or voltage after its SI unit, the Volt) is the difference of electrical potential between two points of an electrical A cathode is an Electrode through which (positive Electric current flows out of a polarized electrical device Electromagnetism is the Physics of the Electromagnetic field: a field which exerts a Force on particles that possess the property of The electron beam that has been transmitted through a specimen that is in part transparent to electrons carries information about the inner structure of the specimen in the electron beam that reaches the imaging system of the microscope. The spatial variation in this information (the "image") is then magnified by a series of electromagnetic lenses until it is recorded by hitting a fluorescent screen, photographic plate, or light sensitive sensor such as a CCD (charge-coupled device) camera. A charge-coupled device ( CCD) is an analog Shift register, that enables the transportation of analog signals (electric charges through successive stages (capacitors The image detected by the CCD may be displayed in real time on a monitor or computer.

Resolution of the TEM is limited primarily by spherical aberration, but a new generation of aberration correctors have been able to partially overcome spherical aberration to increase resolution. spherical-aberration-diskjpg|thumb|300 px|left|A Point source as imaged by a system with negative (top zero (center and positive (bottom spherical aberration Software correction of spherical aberration for the High Resolution TEM HRTEM has allowed the production of images with sufficient resolution to show carbon atoms in diamond separated by only 0. High Resolution Transmission Electron Microscopy ( HRTEM) is an imaging mode of the Transmission electron microscope (TEM that allows the imaging of the crystallographic 89 ångström (89 picometers) and atoms in silicon at 0. An ångström or angstrom (symbol Å) (ˈɔːŋstrəm Swedish: ˈɔ̀ŋstrœm is an internationally recognized non- SI unit of length equal A picometre ( American spelling: picometer, symbol pm) is a unit of Length in the Metric system, equal to one trillionth 78 ångström (78 picometers)^[6][7] at magnifications of 50 million times. ^[8] The ability to determine the positions of atoms within materials has made the HRTEM an important tool for nano-technologies research and development.

Scanning Electron Microscope (SEM)

Main article: Scanning Electron Microscope

Unlike the TEM, where electrons of the high voltage beam form the image of the specimen, the Scanning Electron Microscope (SEM)^[9] produces images by detecting low energy secondary electrons which are emitted from the surface of the specimen due to excitation by the primary electron beam. The scanning electron microscope ( SEM) is a type of Electron microscope that images the sample surface by scanning it with a high-energy beam of Electrons The scanning electron microscope ( SEM) is a type of Electron microscope that images the sample surface by scanning it with a high-energy beam of Electrons In the SEM, the electron beam is rastered across the sample, with detectors building up an image by mapping the detected signals with beam position.

Generally, the TEM resolution is about an order of magnitude greater than the SEM resolution, however, because the SEM image relies on surface processes rather than transmission it is able to image bulk samples and has a much greater depth of view, and so can produce images that are a good representation of the 3D structure of the sample.

Reflection Electron Microscope (REM)

In addition there is a Reflection Electron Microscope (REM). Like TEM, this technique involves electron beams incident on a surface, but instead of using the transmission (TEM) or secondary electrons (SEM), the reflected beam is detected. This technique is typically coupled with Reflection High Energy Electron Diffraction and Reflection high-energy loss spectrum (RHELS). Reflection high-energy electron diffraction ( RHEED) is a technique used to characterize the surface of crystalline materials Another variation is Spin-Polarized Low-Energy Electron Microscopy (SPLEEM), which is used for looking at the microstructure of magnetic domains. A magnetic domain describes a region within a material which has uniform Magnetization. ^[10]

Scanning Transmission Electron Microscope (STEM)

Main article: Scanning Transmission Electron Microscope

The STEM rasters a focused incident probe across a specimen that (as with the TEM) has been thinned to facilitate detection of electrons scattered through the specimen. A scanning transmission electron microscope (STEM is a type of Transmission electron microscope. The high resolution of the TEM is thus possible in STEM. The focusing action (and aberrations) occur before the electrons hit the specimen in the STEM, but afterward in the TEM. The STEM's use of SEM-like beam rastering simplifies annular dark-field imaging, and other analytical techniques, but also means that image data is acquired in serial rather than in parallel fashion. Annular dark-field imaging is a method of mapping samples in a Scanning transmission electron microscope (STEM

Sample Preparation

An insect coated in gold for viewing with a scanning electron microscope.

Materials to be viewed under an electron microscope may require processing to produce a suitable sample. The technique required varies depending on the specimen and the analysis required:

• Fixation for biological specimens.
• Cryofixation – freezing a specimen so rapidly, to liquid nitrogen or even liquid helium temperatures, that the water forms vitreous (non-crystalline) ice. Liquid nitrogen (liquid density at the Triple point is 0707 g/mL is the liquid produced industrially in large quantities by Fractional distillation of Helium exists in Liquid form only at very low Temperatures The Boiling point and critical point depend on the Isotope Amorphous ice is an Amorphous solid form of water meaning it consists of Water molecules that are randomly arranged like the atoms of common Glass. This preserves the specimen in a snapshot of its solution state. An entire field called cryo-electron microscopy has branched from this technique. Electron cryomicroscopy ( cryo-EM or sometimes cryo-electron microscopy) is a form of Electron microscopy (EM where the sample is studied at Cryogenic With the development of cryo-electron microscopy of vitreous sections (CEMOVIS), it is now possible to observe virtually any biological specimen close to its native state. Electron cryomicroscopy ( cryo-EM or sometimes cryo-electron microscopy) is a form of Electron microscopy (EM where the sample is studied at Cryogenic
• Dehydration – replacing water with organic solvents such as ethanol or acetone. Water is a common Chemical substance that is essential for the survival of all known forms of Life. Acetone (also known as propanone, dimethyl ketone, 2-propanone, propan-2-one and β-ketopropane) is a colorless mobile flammable
• Embedding – infiltration of the tissue with a resin such as araldite or epoxy for sectioning. Resin, not to be confused with Rosin, is a Hydrocarbon Secretion of many Plants particularly coniferous trees. Araldite is a registered Trademark of Huntsman Advanced Materials (previously part of Ciba) referring to their range of engineering and structural In Chemistry, epoxy or polyepoxide is a Thermosetting Epoxide Polymer that cures (polymerizes and crosslinks when mixed with a After this embedding process begins, the specimen must be polished to a mirror-like finish using ultra-fine abrasives. The polishing process must be performed carefully to minimise scratches and other polishing artefacts that impose on image quality.
• Sectioning – produces thin slices of specimen, semitransparent to electrons. These can be cut on an ultramicrotome with a diamond knife to produce very thin slices. A microtome is a mechanical instrument used to cut biological specimens into transparent thin sections for microscopic examination In Mineralogy, diamond is the allotrope of carbon where the carbon atoms are arranged in Glass knives are also used because they can be made in the lab and are much cheaper. A glass knife is a Knife with a blade composed of Glass. The cutting edge of a glass knife is formed from a fracture line and is extremely sharp
• Staining – uses heavy metals such as lead, uranium or tungsten to scatter imaging electrons and thus give contrast between different structures, since many (especially biological) materials are nearly "transparent" to electrons (weak phase objects). Characteristics Lead has a dull luster and is a dense, Ductile, very soft highly Uranium (jʊˈreɪniəm is a silvery-gray Metallic Chemical element in the Tungsten (ˈtʌŋstən also known as wolfram (/ˈwʊlfrəm/ is a Chemical element that has the symbol W and Atomic number 74 In biology, specimens are usually stained "en bloc" before embedding and also later stained directly after sectioning by brief exposure to aqueous (or alcoholic) solutions of the heavy metal stains.
• Freeze-fracture or freeze-etch – a preparation method particularly useful for examining lipid membranes and their incorporated proteins in "face on" view. The fresh tissue or cell suspension is frozen rapidly (cryofixed), then fractured by simply breaking or by using a microtome while maintained at liquid nitrogen temperature. The cold fractured surface (sometimes "etched" by increasing the temperature to about -100°C for several minutes to let some ice sublime) is then shadowed with evaporated platinum or gold at an average angle of 45° in a high vacuum evaporator. A second coat of carbon, evaporated perpendicular to the average surface plane is often performed to improve stability of the replica coating. The specimen is returned to room temperature and pressure, then the extremely fragile "pre-shadowed" metal replica of the fracture surface is released from the underlying biological material by careful chemical digestion with acids, hypochlorite solution or SDS detergent. The still-floating replica is thoroughly washed from residual chemicals, carefully fished up on EM grids, dried then viewed in the TEM.
• Ion Beam Milling – thins samples until they are transparent to electrons by firing ions (typically argon) at the surface from an angle and sputtering material from the surface. An ion is an Atom or Molecule which has lost or gained one or more Valence electrons giving it a positive or negative electrical charge This article pertains to the chemical element For other uses see Argon (disambiguation. A subclass of this is Focused ion beam milling, where gallium ions are used to produce an electron transparent membrane in a specific region of the sample, for example through a device within a microprocessor. Focused ion beam, also known as FIB, is a technique used particularly in the semiconductor and materials science fields for site-specific analysis deposition and ablation of Gallium (ˈgæliəm is a Chemical element that has the symbol Ga and Atomic number 31 Ion beam milling may also be used for cross-section polishing prior to SEM analysis of materials that are difficult to prepare using mechanical polishing.
• Conductive Coating – An ultrathin coating of electrically-conducting material, deposited either by high vacuum evaporation or by low vacuum sputter coating of the sample. This is done to prevent the accumulation of static electric fields at the specimen due to the electron irradiation required during imaging. Such coatings include gold, gold/palladium, platinum, tungsten, graphite etc. and are especially important for the study of specimens with the scanning electron microscope. Another reason for coating, even when there is more than enough conductivity, is to improve contrast, a situation more common with the operation of a FESEM (field emission SEM). When an osmium coater is used, a layer far thinner than would be possible with any of the previously mentioned sputtered coatings is possible. [1]

Disadvantages

Pseudocolored SEM image of the feeding basket of Antarctic krill. Antarctic krill ( Euphausia superba) is a Species of Krill found in the Antarctic waters of the Southern Ocean. Real electron microscope images do not carry any color information, they are greyscale. In Computing, a grayscale or greyscale Digital image is an image in which the value of each Pixel The first degree filter setae carry in v-form two rows of second degree setae, pointing towards the inside of the feeding basket. Seta (plural setae) is a biological term derived from the Latin word for " Bristle " The purple ball is one micrometer in diameter. To display the total area of this structure one would have to tile this image 7500 times.

Electron microscopes are expensive to build and maintain. They are dynamic rather than static in their operation: requiring extremely stable high-voltage supplies, extremely stable currents to each electromagnetic coil/lens, continuously-pumped high- or ultra-high-vacuum systems, and a cooling water supply circulation through the lenses and pumps. As they are very sensitive to vibration and external magnetic fields, microscopes aimed at achieving high resolutions must be housed in buildings (sometimes underground) with special services. Some desktop low voltage electron microscopes have TEM capabilities at very low voltages (around 5 kV) without stringent voltage supply, lens coil current, cooling water or vibration isolation requirements and as such are much less expensive to buy and far easier to install and maintain, but do not have the same ultra-high (atomic scale) resolution capabilities as the larger instruments.

The samples largely have to be viewed in vacuum, as the molecules that make up air would scatter the electrons. This vacuum means "absence of matter" or "an empty area or space" for the cleaning appliance see Vacuum cleaner. One exception is the environmental scanning electron microscope, which allows hydrated samples to be viewed in a low-pressure (up to 20 torr), wet environment. The torr (symbol Torr) is a non- SI unit of Pressure defined as 1/760 of an atmosphere.

Scanning electron microscopes usually image conductive or semi-conductive materials best. Non-conductive materials can be imaged by an environmental scanning electron microscope. A common preparation technique is to coat the sample with a several-nanometer layer of conductive material, such as gold, from a sputtering machine; however, this process has the potential to disturb delicate samples. Gold (ˈɡoʊld is a Chemical element with the symbol Au (from its Latin name aurum) and Atomic number 79

The samples have to be prepared in many ways to give proper detail, which may result in artifacts from such treatment. In Natural science and Signal processing, an artifact is any perceived Distortion or other Data error caused by the instrument of observation This raises the problem of distinguishing artifacts from material, particularly in biological samples. Foundations of modern biology There are five unifying principles It is generally believed by scientists working in the field that as results from various preparation techniques have been compared and that there is no reason that they should all produce similar artifacts, it is reasonable to believe that electron microscopy features correlate with living cells. In addition, higher-resolution work has been directly compared to results from X-ray crystallography, providing independent confirmation of the validity of this technique. X-ray crystallography is a method of determining the arrangement of Atoms within a Crystal, in which a beam of X-rays strikes a crystal and scatters Since the 1980s, analysis of unfixed, vitrified specimens has also become increasingly used by scientists, further confirming the validity of this technique. ^[11], ^[12], ^[13]

Electron microscopy application areas

Semiconductor and data storage Circuit edit 3D metrology Defect analysis Failure analysis Biology and life sciences Cryobiology Protein localization Electron tomography Cellular tomography Cryo-electron microscopy Toxicology Biological production and viral load monitoring Particle analysis Pharmaceutical QC 3D tissue imaging Virology Vitrification

Research Materials qualification Materials and sample preparation Nanoprototyping Nanometrology Device testing and characterization Industry High-resolution imaging 2D & 3D micro-characterization Macro sample to nanometer metrology Particle detection and characterization Direct beam-writing fabrication Dynamic materials experiments Sample preparation Forensics Mining (mineral liberation analysis) Chemical/Petrochemical

See also

• Category:Electron microscope images
• Field emission microscope
• Scanning tunneling microscope

References

External links

• Environmental Scanning Electron Microscope (ESEM)
• X-ray element analysis in electron microscope – Information portal with X-ray microanalysis and EDX contents
• John H.L. Watson: Very early Electron Microscopy in the Department of Physics, the University of Toronto – A personal recollection
• Rubin Borasky Electron Microscopy Collection, 1930-1988 Archives Center, National Museum of American History, Smithsonian Institution.
• electron microscopy Website of the ETH Zurich: Very good graphics and images, which illustrate various procedures.
• Albert Lleal microphotography. Scanning Electron Microphotography Coloured SEM